Fluid cell press with a gripping arrangement and method and use of the press

ABSTRACT

The present invention relates to a method in a press of pressure cell type comprising a forming tool and, separated therefrom, a diaphragm, which define a forming space in which a blank is inserted for forming thereof against the forming tool by pressing the diaphragm against the blank. A blank portion projecting from the forming space is gripped by means of at least one gripping device and the connection between the blank and the gripping device is shielded from the diaphragm at least when the diaphragm is pressed against the blank. The invention further relates to a press of pressure cell type and a tray device.

FIELD OF THE INVENTION

The present invention relates to a press of pressure cell type and amethod in such a press. The invention further relates to a tray device.

BACKGROUND ART

A press of pressure cell type generally comprises a force-absorbingpress body defining a press chamber. In the upper part of the presschamber, a press plate and a diaphragm of rubber or another resilientmaterial are arranged, which together form a pressure cell. The pressurecell communicates with a source of pressure and expands when a pressuremedium is supplied. In the lower part of the press chamber, a structuralsupport or a tray is usually arranged, which comprises a bottom platehaving a tray frame. The tray supports a forming tool, a workpiece orblank to be machined, and, generally, a mat of rubber or anotherresilient material covering the forming tool and the blank.

Presses of pressure cell type are used, among other things, when formingsheet-shaped blanks or workpieces, for example sheets of steel oraluminium, to short-series products within the aerospace and automotiveindustries. The sheet is placed in the press in such manner that one ofits sides faces a forming tool. The resilient diaphragm is arranged onthe other side of the sheet. A closed space between the diaphragm andthe press plate located above the diaphragm constitutes the pressurecell and this space is filled during the forming process with a pressuremedium. By pumping additional pressure medium into the pressure cell,the pressure is increased in the pressure cell and the resilientdiaphragm is pressed during stretching against the sheet which, in itsturn, is formed round or in the forming tool. When the sheet completelyfits to the forming tool, the pressure in the pressure cell is releasedand the diaphragm is removed, following which the formed component canbe taken out of the press. It is often desirable to obtain an efficienthandling of the production flow and, thus, short cycle times.

SUMMARY OF THE INVENTION

One object of the present invention is to provide more efficientoperation of a press of pressure cell type.

Another object of the invention is to provide a simple method ofoperating a press of pressure cell type.

These and other objects, which will be evident from the followingdescription, are achieved by means of a press of pressure cell type anda method, which have the features indicated in the appended claims.

According to one aspect of the invention, a method is provided in apress of pressure cell type comprising a forming tool and, separatedtherefrom, a diaphragm, which define a forming space in which a blank isinserted for forming thereof against the forming tool by pressing thediaphragm against the blank. According to the method, a blank portionprojecting from the forming space is gripped by means of at least onegripping device, and the connection between the blank and the grippingdevice is shielded from the diaphragm at least when the diaphragm ispressed against the blank.

Thus, the present invention is based on the understanding that theoperation of a press of pressure cell type can be rendered moreeffective compared with existing forming methods by using at least onefurther measure in the form of shielding the connection between theblank and the gripping device. Incorporating such an additional measureis contrary to the general approach according to which the eliminationof measures is what makes the operation less time-consuming and moreefficient. Surprisingly, however, it has been found that providingshielding according to the method of the invention may result in anoverall saving of time. One reason for this is that, during repeatedpressing operations, the diaphragm, even when protected from below by amat, risks being damaged or worn progressively as it comes in contactwith edges and penetrates into slots, thus requiring a time-consumingoperation to replace the diaphragm to be carried out. By shielding theconnection between the blank and the gripping device, the diaphragmcannot extend to said connection and, thus, does not risk being damaged.Moreover, as will be described below, shielding can be achievedessentially simultaneously with at least one other measure.

According to a further aspect of the present invention, a press ofpressure cell type is provided. At least one gripping device is arrangedto grip a blank portion projecting from the forming space, and shieldingmeans are arranged to shield the connection between the blank and thegripping device from the diaphragm at least when the diaphragm ispressed against the blank. As will be described below, said shieldingmeans can be effectively incorporated into the press.

In the present application, forming space means the space in which ablank is to be formed between the diaphragm and the forming tool. Theconnection between the sheet and the gripping device forms the borderarea in which the sheet enters the gripping device.

It may be appropriate, in particular when forming a sheet-metal blank,to stretch the blank beyond its yield point to obtain a plasticdeformation thereof. This is achieved, for example, by arranging theblank between two gripping devices and stretching it by means of saiddevices before the diaphragm is allowed to press against the blank.Consequently, the blank has one connection to a gripping device andanother connection, for example in a second end portion of the blank, toanother gripping device. If the distance between these two connectionsis increased after the blank has been gripped, the blank will bestretched. It should be noted that to stretch the blank it is enough todisplace one of the connections, for instance by causing one of thegripping devices to move. According to at least one embodiment of theinvention, the stretching operation is carried out essentiallysimultaneously with the shielding. According to at least one furtherembodiment of the invention, the connection is shielded afterstretching, but before the diaphragm is pressed against or enters intocontact with the blank.

Shielding can be achieved, after the blank has been stretched, ifapplicable, for example by moving two shielding members, one on eachside of the blank, towards each other and applying a compressive forceto the shielding members in said direction. The compressive force has tobe large enough to obtain a sufficiently tight abutment between theshielding members and the blank, i.e. a seal that will resist thepressure of the diaphragm and prevent the diaphragm from extendingbetween the shielding members and the blank to said connection. Theshielding members can be brought together even if it is desirable tostretch the blank, as long as they do not prevent the blank from beingstretched. For example, they could abut against the blank without anycompressive force having yet been applied thereon. Alternatively, theshielding members can be designed, as will be described below, in suchmanner that it is possible to stretch the blank even if the compressiveforce is applied.

It should be noted that unlike clamps, pinches or other forms ofgripping devices, which are susceptible of receiving both a blank and adiaphragm, the variant of the shielding member described above may beinfluenced by an applied compressive force, which ensures that thegripping device receives the blank only. As will be shown, even thediaphragm itself may contribute to the application of said force. Thecompressive force is maintained until there is no longer any risk of thediaphragm penetrating in the connection between the blank and thegripping device.

A lower shielding member is conveniently arranged on the tray bottom,for example adjacent the forming tool, and the blank is then placedabove said member and gripped by means of the gripping device andstretched, if applicable. An upper shielding member is lowered and,suitably, pressed against the lower shielding member and theintermediate blank. The compressive force is achieved, for example, bymeans of hydraulic pistons. In this case, the shielding members, or atleast portions thereof, are preferably situated in front of theconnection between the blank and the gripping device, i.e. between theconnection and the forming tool.

The operation of bringing together the shielding members as describedabove can also be used in connection with the actual gripping of theblank, thus resulting in a more efficient and time-saving operation. Bybringing together not only the shielding members, but simultaneously anupper part and a lower part of the gripping device, the blank can befixed during this motion.

For instance, fixing can be achieved with the aid of force-exertingmeans, such as hydraulic pistons. A force is applied to at least one ofthe shielding members, on both sides of the horizontal extent of theblank and/or gripping device transversely to the stretching direction,said force being directed towards the other shielding member. Theseforces, which are thus-applied along the periphery of the shieldingmembers, located outside the blank and/or the gripping device in thestretching plane, exert a pressure on the gripping device in such mannerthat the blank is fixed by said gripping device.

Preferably, the upper shielding member is bent in such manner that itscentral portion is located vertically lower than peripheral portions towhich said forces are applied. When the forces are applied, the uppershielding member is straightened and an evenly distributed pressure willbe exerted on the gripping device below.

Suitably, the two shielding members are sufficiently separated in frontof the connection of the blank to allow the blank to be stretched, i.e.there is a gap between the front portions of the shielding members thatare not in contact with the gripping device. During the actual pressingof the diaphragm, the press load will close the gap enough to preventthe diaphragm from penetrating through it. Preferably, the diaphragmitself is used in this operation by exerting a pressure, during itsexpansion, on the upper shielding member to reduce the gap.

The upper part of the gripping device is suitably connected to an uppershielding member, so that they are lowered together onto the blank oncethe blank has been arranged on the lower part of the gripping device.Similarly, the upper part of the gripping device can preferably belifted together with the upper shielding member, thus allowing quick andeasy release of a finished blank.

Preferably, the shielding members are designed in such manner that they,when brought together, enclose the gripping device from above and frombelow, thus creating a space for the gripping device. Suitably, thespace is large enough to allow the gripping device to be moved so that ablank fixed therein can be stretched. The gripping device is suitablymoved radially outwards from the forming space. Owing to thisencapsulation, the moving parts of the gripping device are thusrelatively well protected from other elements also during stretchingand, in particular, when the compressive force is applied to theshielding members. Moreover, the encapsulation allows the grippingdevice to be moved without a gap or a space being formed in which adiaphragm could penetrate.

The upper and the lower shielding member preferably have displacementsurfaces, such as sliding surfaces on which respectively the upper andthe lower part of the gripping device are slidable. A displacementsurface can be achieved in various ways, for example by means of planesurfaces, grooves, ball bearings, etc.

When the gripping device is displaced in the space formed by theshielding member, the upper and the lower part are preferablyinterconnected and, thus, simultaneously displaced. The interconnectioncan be achieved, for example, by one of the parts having a bead or bosswhich fits in a hollow or dent in the other part. If the upper and thelower part of the gripping device are interconnected in the assembledposition, then only one of them has to be subjected to a moving force,for example in the form of an external pulling device.

Preferably, a fixed stop is provided in or at said formed space, so thatthe gripping device cannot be displaced any further than this stop. Sucha fixed stop ensures satisfactory repeatability and thereby allowsblanks to be equally stretched even if they are stretched at differentmoments.

According to at least one embodiment of the invention, the forming toolis arranged in a tray device provided in a press, which tray device canbe divided into an upper and a lower tray part, the blank being grippedby the upper and the lower tray part being brought together. Suitably,the shielding members are also brought together in connection with sucha movement of the tray parts. In this case, the upper shielding memberis connected to the upper part of the tray device to allow them to belifted and/or lowered together.

An upper tray part can comprise, for example, part of a tray side, suchas a beam which can be lifted from the rest of the tray. Suitably, twodifferent side beams are liftable, for instance one from eitherlongitudinal side of a tray. The upper shielding member is thenconnected to these side beams and extends between them. If the shortside forms an indivisible piece, or even an integrated portion of saidremaining part of the tray, such a short side is provided with a throughhole through which the gripping device is accessible to an externalpulling device to allow the blank to be stretched.

Instead of lifting only side beams of the tray, a whole annular part ofthe tray may be liftable and lowerable. Consequently, according to atleast one embodiment of the invention, the tray device comprises a trayplate and a tray frame, said tray frame being annularly divisible intoat least one upper frame part and one lower frame part. Annularlydivisible here means that the parts are annular in cross section, i.e.they have the shape of a closed path around a central hollow space. Anannular shape can be, circular, elliptic, straight long sides tosemi-circular short sides, etc. Suitably, the upper shielding member isconnected to the upper frame part to allow them to be lifted and/orlowered together. Moreover, the blank is preferably clamped or grippedin a corresponding manner. When the upper frame part has been lifted,thus exposing the lower tray part on which the lower part of thegripping device is arranged, an outer portion of the blank is arrangedthereon. Then, as the upper frame part is lowered together with theupper part of the gripping device connected thereto, the upper and thelower part of the gripping device will fix the blank between them. Atthe same time, the entire tray frame is reassembled by the frame partshaving been brought together.

When the pressing operation has been completed, the upper and the lowertray part are preferably separated by displacing said parts in relationto one another along the common centre axis direction of the parts, sothat a space is formed between them. For instance, an upper frame partis lifted from a lower frame part, so that a processed blank isaccessible for removal thereof, and so that, after removal of theprocessed blank, a new blank can be arranged in the tray device. Analternative to a straight lifting motion can be a turning motion, or amotion similar to opening a hatch, more or less corresponding to themotion of a trouser press.

It will be apparent from the above that a divisible tray device allowsrapid fitting of a new blank, and also rapid removal of a finishedblank, while at the same time the actual gripping of the blank isachieved in a simple manner. In addition, the displacement of theshielding members can be used advantageously in combination with thedivisible tray device.

An efficient process is obtained if the tray device is taken out of thepress before it is separated into said parts. A second tray device, inwhich a blank has already been fitted, can be simultaneously inserted inthe press to be formed therein. While said blank is being formed in thepress, the finished blank is removed from the tray device that has beentaken out and replaced by a new, unprocessed blank. The separated partsof the tray device located outside the press are then brought togetherso that the device is ready for a new pressing operation.

Although it may be preferred to separate the tray parts outside thepress, said parts can alternatively be separated and/or brought togetherinside the press chamber.

In the tray disposed in presses of pressure cell type, filling elementsor end pieces are sometimes provided, for example at the short sides ofthe tray. In addition, resilient supports that are parallel to the mainaxis of the press chamber can be arranged adjacent the long sides of thetray. These end pieces and supports are made of a resilient material,such as rubber, and are thus fitted next to the forming tool. The endpieces serve as a support for the forming tool. They also have aprotective function, since they protect the tray frame and prolong itsservice life, which is advantageous in particular in the case of a trayframe that is divisible into at least one upper and one lower framepart, as described above.

Advantageously, end pieces can be used also in connection with thepresent invention by integrating the shielding members in an end piece.Thus, an end piece can be divisible into an upper and a lower part.While the lower part is intended to remain on the bottom of the tray, inconventional manner, the upper part can be lifted and act as the uppershielding member. The upper part of the gripping device is convenientlyarranged in said upper end piece. As described above in connection withthe shielding members, the upper and the lower part of the end piecepreferably form a space in which the gripping device is movable.

Preferably, use is made of at least two divisible end pieces asdescribed above, said end pieces being arranged at two opposite sides ofthe inner wall of the tray device and serving as a support for theforming tool. The blank is thus placed over the forming tool and clampedon either side by means of the end pieces and the gripping devicesarranged therein. If a smaller forming tool is to be used, the dimensionof which is smaller than the available space between the end pieces, oneof the end pieces is suitably moved away from the inner wall towards thecentre of the tray device to abut against and support the small formingtool.

In the case where use is made of a divisible tray device, as describedabove, an upper part of each end piece is suitably integrated with or atleast connected to the upper tray part. As mentioned above, the uppertray part may consist of either two side beams or an annular upper framepart. When the upper tray part is lifted, so are the upper part of theend pieces and, conveniently, also the upper part of each grippingdevice.

In the variant involving end pieces, as in other variants, only one ofthe gripping devices, or the connection of the blank thereto, needs tobe movable in order to allow the blank to be stretched. According to atleast one preferred embodiment of the present invention, use is made ofa hydraulic arrangement comprising a hydraulic piston and a couplingmeans connected thereto. The coupling means, which can consist of an armor a plate, is further connected to at least one of the parts of thegripping device, such as the upper or the lower part. The hydraulicpiston is adapted to actuate the coupling means and, thus, the grippingdevice for stretching the fixed blank. In the case where one fixed endpiece and one movable end piece are used, the hydraulic arrangement issuitably adapted to actuate the gripping device in the fixed end piece.

It follows from the above that, according to a third aspect of theinvention, a tray device is provided for use in a press of pressure celltype, which tray device defines a space adapted to receive a formingtool against which a blank is formable. The tray device is thuscharacterised by at least one gripping device, which is adapted to gripan end portion of the blank, and shielding members, which are guidablebetween an open position and a shielding position and which are adaptedto at least partially enclose the gripping device in the shieldingposition.

The above description emphasizes the fact that the gripping devicecomprises two parts which can be separated and then brought together.However, other alternative embodiments are conceivable. For instance,the gripping device can be provided with a slot which extends from theperiphery of the gripping device, for example towards its centre. If thegripping device is circular in cross-section, the slot may extendradially from the periphery towards the centre of the gripping device.The blank portion projecting from the forming space is thus gripped byinserting it through the slot. The slot may optionally be inwardlytapered.

The shield of a gripping device which is circular in cross-section andhas a slot that extends inwards from the circumferential surface ispreferably rotatable about its centre axis. Such a rotation causes ablank portion inserted in the slot to move and can be compared with aninitial wrapping or winding of the blank around the gripping device.Consequently, the blank is stretched when the gripping device isrotated. Moreover, the gripping device can be at least partiallyenclosed by a wall in tight abutment against the gripping device, saidwall having a suitable cross section, which means that after a certaindegree of rotation the slot faces the wall and, as a result, theconnection between the blank and the gripping device is shielded. Inthis case, the wall can be considered to make up at least part of ashielding member, and shielding of the connection between the blank andthe gripping device is achieved essentially simultaneously with thestretching of the blank.

The present invention is particularly suitable for forming asheet-shaped blank, such as sheet steel, into a relatively flat objector a large surface object. Objects of this type are, for example, carroofs, hoods, parts of an aircraft wing.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 is a cross-sectional perspective view of a portion of a traydevice in a press of pressure cell type.

FIG. 2 is a cross-sectional side view of a portion of a press ofpressure cell type with a tray device in two positions.

FIG. 3 is a cross-sectional top view of the portion of the press shownin FIG. 2.

FIG. 4 is a schematic illustration of one example of stretching of aclamped sheet-metal blank.

FIGS. 5 a and 5 b illustrate a method of shielding the connectionbetween a blank and a gripping device.

FIGS. 6 a and 6 b illustrate alternative methods for shielding andgripping arrangements.

FIGS. 7 a and 7 b illustrate the handling of an alternative tray device.

FIG. 8 illustrates possible ways of changing the dimensions of a traydevice.

FIGS. 9 a and 9 b are cross-sectional views of a gripping and shieldingarrangement according to one embodiment of the present invention.

FIG. 10 is a perspective view of the arrangement in FIG. 9 a.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional perspective view of a tray device 10 in apress of pressure cell type. The tray device 10 comprises a bottom plateor tray plate 12 and a tray frame. The tray frame comprises threeannular, plate-shaped lamellar means 14 a, 14 b, 14 c, which areconcentrically arranged one above the other. Each lamellar means has twoparallel long sides 16 (part of one long side is shown), the section inthe figure being taken along a line that is parallel to the long sides,and two rounded, semi-circular short sides 18 (part of one short side isshown), which together define an inner space. The external surface ofeach lamellar means 14 a, 14 b, 14 c is provided with a prestressing,preferably band-shaped winding 20 adapted to absorb loads duringpressing. Thus, this force-absorbing winding is not separate from thetray frame but integrated therewith.

In the space defined by the tray frame, a forming tool 22 is arranged onwhich a sheet 24 is to be formed. In the basic configuration, thelamellar means 14 a, 14 b, 14 c are brought together in such manner thatthere is essentially no air gap between them. On the other hand, beforea pressing operation, the sheet 24 is clamped between the uppermostlamellar means 14 a and the lamellar means 14 b located immediatelybelow. The sheet 24 extends above the forming tool 22 across the definedspace.

An end piece is arranged between the forming tool 22 and the inner wallon the short side 18 of the tray frame to support the forming tool. Theend piece comprises an upper part 26, which is connected to theuppermost lamellar means 14 a, and a lower part 28, which rests on thetray plate 12. When brought together, the upper 26 and the lower 28 partof the end piece form a sliding space 30 in which a locking or grippingdevice is displaceable. The gripping device comprises an upper part 32and a lower part 34, between which the sheet 24 is clamped. The upperpart 32 of the gripping device is connected to the upper part 26 of theend piece, while its lower part 34 abuts against the lower part 28 ofthe end piece. The gripping device is moved in the space by means of ahydraulic arrangement. The hydraulic arrangement comprises a hydraulicpiston 36 which actuates a plate 38 connected to the gripping device.Accordingly, when the plate 38 is caused to move, the gripping device32, 34 connected thereto will also move, which results in the fixedsheet 24 being stretched.

A protective mat 40, indicated by phantom lines, is arranged to coverthe forming tool 22 and the sheet 24 and protects a diaphragm (notshown) to limit the wear thereof. The mat 40 rests on the upper side ofthe end pieces in the tray device. The diaphragm is located above theprotective mat 40 and adapted to expand and press the sheet 24 locatedunderneath against the forming tool 22. The surface of the forming toolis machined and provided with recesses having sharp edges, which act ascutting devices to cut or trim the sheet. Under low pressures, the areaaround the edge of the sheet is pressed against a first cutting device42 a. This is achieved by a punch 44 arranged above the cutting device42 a forcing the sheet 24 down towards the cutting device. Thediaphragm, which is expanded during pressing, then presses the punch 44against the sheet 24, which is pressed down into the first cuttingdevice 42 a, the outer edge of the sheet being cut off. When thepressure increases, a fine trimming takes place in a second cuttingdevice 42 b, which is a stepped recess. The sheet 24 is thus cut off atthis cutting device 42 b, following which the pressure is furtherincreased to a maximum pressure, such as 1400 bar, and the sheet is thusgiven its final shape, for example that of a car roof.

FIG. 1 further shows that the upper part 26 of the end piece has aportion 46 which extends beyond the circumference of the lamellar means14 a to which the upper part 26 is connected. This projecting portion 46has several functions. When this portion 46 is lifted, suitably togetherwith the corresponding portion of the end piece (not shown) arranged atthe other short side, the whole uppermost lamellar means 14 a as well asupper parts 26 of the respective end pieces connected thereto, includingthe upper part 32 of the gripping device, are raised so that they areseparated from the remaining elements located underneath. The projectingportion 46 is also used to shield the connection between the sheet 24and the gripping device 32, 34 from the diaphragm. By applying adownward force to said projecting portion 46, for example by means ofhydraulic pistons, the upper part of the end piece 26 will bear againstthe lower part 28, and the sheet 24 arranged between them, with enoughforce to prevent the diaphragm from penetrating between them.Alternatively, the downward force will contribute mainly to clamping theblank between the upper and lower part of the gripping device, while agap between the upper 26 and lower 28 parts of the end piece will allowthe sheet 24 to be stretched, the gap being closed only afterstretching. The forces thus exerted are illustrated schematically inFIGS. 5 a and 5 b.

FIG. 2 is a cross-sectional side view of a portion of a press ofpressure cell type in two positions. The left part of the figureillustrates a position before the forming of a sheet, i.e. when the traydevice is situated inside the press of pressure cell type, while theright part of the figure illustrates a position after the forming of thesheet, i.e. when the tray device has been removed from the press ofpressure cell type. Similar reference characters are used to designateparts in FIG. 2 and FIGS. 3-5 which correspond to those in FIG. 1.

Thus, in the left part of FIG. 2 a tray device is shown comprising atray plate 12 and a tray frame, which comprises four concentric lamellarmeans 14 a, 14 b, 14 c, 14 d arranged one above the other. Compared withFIG. 1, a further lamellar means 14 d has thus been added. The number oflamellar means can be chosen depending on the desired working depth forthe forming process concerned. As in the case of the tray device shownin FIG. 1, the lamellar means in the tray device according to FIG. 2 arewound with bands inside which an end piece having an upper part 26 and alower part 28 is arranged. Moreover, an upper part 32 and a lower part34 of a gripping device act to hold a sheet 24 projecting from theforming space, which is defined by a forming tool 22 resting on the traybottom and a diaphragm 48 arranged above the latter. The diaphragm 48forms, together with an upper press plate 50 and a vessel wall 52, apressure cell, which can be filled with a liquid, such as water or oil,as indicated in the figure. The liquid is supplied through a valve 54.The edge zone of the diaphragm 48 is sealed so that no liquid can passthe diaphragm and force its way out of the pressure cell. Whenadditional liquid is supplied to the pressure cell it will expand by thediaphragm 48 expanding downwards and pressing the sheet 24 against theforming tool 22. In the same way as described with reference to FIG. 1,shielding of the diaphragm is achieved, preferably before the diaphragm48 has started its downward expansion, by the upper part 26 of each endpiece being pressed against the lower part 28. Moreover, a protectivemat 40 is arranged between the sheet 24 and the diaphragm 48, said mat40 resting on the upper side of the end pieces.

It should be noted that the tray frame, i.e. the lamellar means 14 a, 14b, 14 c, 14 d, as shown in FIG. 2, extends beyond the vessel wall 52and, thus, has no force-absorbing means on the short sides (the sectionin the figure is taken along a line that is parallel to the long sidesof the tray device). The prestressing provided by the wound bands 20 incombination with the rounded shape of the short sides is enough towithstand the internal forces generated during a pressing operation.

The right part of FIG. 2 illustrates a situation after the sheet 24 hasbeen formed. The tray device has been laterally displaced and removedthrough an end piece of the press of pressure cell type. Outside thepress of pressure cell type, the formed sheet has been made accessibleby lifting the uppermost lamellar means 14 a, and thus also the upperpart of the end piece 26′ with the protective mat 40 resting thereon aswell as the associated punch 44 and upper part 32′ of the grippingdevice. One advantage of the annular divisibility of the tray frame isthat the protective mat 40 is rapidly and easily removed from the sheet.In prior art, use has been made, for instance, of more complicateddevices by means of which the mat is rolled up only to be rolled outlater before the next forming operation.

In the tray device shown in FIG. 2, the gripping devices on both shortsides are connected to a hydraulic arrangement 36, 36′, 36, 38′, whichallows the sheet to be stretched by pulling on one or both sidesthereof.

FIG. 3 is a cross-sectional top view of the portion of the press shownin FIG. 2. The section is taken along the line III-III in FIG. 2. Theleft part of FIG. 3 shows how the protective mat 40 covers the wholesheet and the forming tool 22. Furthermore, the extension of the endpiece is indicated by a dashed line 56. The end piece thus has the shapeof a half moon or a filled semicircle, its rounded portion following theinside of the rounded portion of the tray frame, i.e. the short side 18.Together with the long sides 16 of the tray frame, the straight portionof said end piece, like that of the end piece provided at the othershort side 18′ of the tray device, forms a rectangular space in whichthe forming tool 22 is disposed. In the right part of FIG. 3, thesurface irregularities of the forming tool are shown in the form ofrecesses, i.e. the cutting devices 42 a, 42 b mentioned above. FIG. 3further shows that the bottom or tray plate 12 on which the lamellarmeans are arranged is essentially quadrangular and that its length andwidth correspond essentially to the length and width of the lamellarmeans (only the uppermost lamellar means 14 a is shown in the figure).The lamellar means are shaped like a race track, i.e. two long sides 16(only one is shown) and two short sides 18, 18′ in the form of convexsemicircles. The lamellar means are wound with bands, the thickness ofthe layer of bands 20 being about 100 mm.

FIG. 4 illustrates schematically one example of stretching of a clampedsheet-metal blank. The figure shows a forming tool 22 and an end piece26, 28 resting on a tray plate 12. The tray frame is not shown. The endpiece comprises a lower part 28, which is considerably larger than anupper part 26 or a cap. The end piece has one side which faces theforming tool 22, here called inside 58, and an opposite side, herecalled outside 60. The lower part 28 and the upper part 26 of the endpiece have upwardly and downwardly projecting portions 62 a, 62 b, 64 a,64 b both on the inside 58 and the outside 60 of the end piece. Theprojecting portions 62 a, 64 a on the inside 58 are thicker than theportions 62 b, 64 b on the outside 60, because the inside 58 is expectedto be exposed to greater forces. Owing to these projecting portions, asliding space 30 is formed when the parts 26, 28 of the end piece arebrought together. A gripping device 32, 34 is slidingly arranged in saidsliding space 30.

A sheet 24 to be formed against the forming tool is arranged in suchmanner that it also extends through a gap between the projectingportions 62 a, 64 a on the inside 58 of the end piece and penetratesbetween an upper 32 and a lower 34 part of the gripping device. The gapbetween the projecting portions 62 a, 64 a on the inside 58 of the endpiece may typically be as small as about 0.10-0.15 mm, which basicallyprevents a diaphragm from penetrating through the gap while allowing athin sheet-metal blank 24 to be stretched. The lower part 34 of thegripping device has a bulge or boss 66 which fits in a hollow 68 or dentin the upper part 32. In the joined position shown, the boss 66 and thehollow 68 form a connection, which allows the parts 32, 34 of thegripping device to be moved simultaneously even if only one of the partsis directly actuated by a moving force, such as an external pullingdevice. An external pulling device preferably comprises an arm or platewhich, in this case, is connected to the gripping device. A pull ram 36is connected to the plate 38 with the aid of which it can actuate thegripping device 32, 34 causing it to move, thereby allowing the clampedsheet 24 to be stretched beyond its yield point. In this phase, theupper 26 and the lower 28 part of the end pieces are not tightlycompressed, but allow the sheet 24 to be stretched. It is not untilafter this that they are supposed to abut sealingly against the sheet sothat its connection 70 to the gripping device, i.e. the side facing theforming tool 22, is shielded from the diaphragm when the latter is beingused for forming the sheet 24. Examples of a gripping device and apulling device will be described in more detail below with reference toFIGS. 9 a-9 b and FIG. 10.

In general, it may be difficult to provide a uniform blocking of thesheet, which is desirable, in particular if the sheet is wide. However,a method will be described below according to which an even distributionof the pressure over the whole clamping area is obtained in a simplemanner. FIGS. 5 a and 5 b illustrate a method of providing shielding ofthe connection between a sheet-metal blank and a gripping device as wellas how to provide fixing of the sheet in a suitable manner. FIG. 5 a isa cross-sectional view along the line V-V in FIG. 4. After the sheet 24has been disposed on the lower part 34 of the gripping device, and afterthe upper part 32 of the gripping device and the upper part 26 of theend piece have been arranged on top of that, peripheral downward forcesF are applied to the upper part 26 of the end piece. The upper part 26of the end piece has the shape of a bow, i.e. it is slightly bent. Itscentral portion is located about 6 mm below it outer edges. Owing tothis design, when a force is applied to the upper part 26 of the endpiece outside the extension of the sheet, it is possible to obtain aneven distribution of the pressure exerted on the upper part 32 of thegripping device, the sheet 24 thus being blocked by an even pressureover the whole blocking area.

The two forces, indicated by arrows F, typically exert-a load of 20 tons(about 200 kN) each, i.e. a total of 40 tons (about 400 kN) distributedover a typical width of 1.6 m, as illustrated in FIG. 5 b. The upperpart 26 of the end piece has a thickness of about 100 mm, a weight ofabout 500 kg, and a dimension in the stretching direction of about 0.5m, and it is made of a steel material which is rigid enough to providethe effect described above. In addition to the advantage of allowing aneven compression of the sheet, this peripheral application of forcesalso has the advantage of allowing forming of a wide sheet.

Following the application of the forces F, which blocks the sheet, thestretching operation is carried out. This is possible because theprojecting portions 62 a, 64 a (see FIG. 4) on the inside 58 of the endpiece are so dimensioned that after compression there is still a gapbetween them which allows the sheet 24 to be stretched. The gap can besmall enough to provide a shield against the diaphragm. However, theprojecting portion 64 a of the upper part 26 of the end piece willusually be deflected during the actual forming of the blank, since loadsamounting to, for example, 1000 bar will act on this portion. Thus, whenthe diaphragm starts to expand it may press down the upper part 26 ofthe end piece causing it to abut in a completely sealing manner againstthe sheet 24.

FIGS. 6 a and 6 b illustrate alternative methods for shielding andgripping arrangements. FIG. 6 is a cross-sectional view of a cylindricalgripping device 80. As shown, the gripping device 80 is circular incross-section and has a central axis of rotation 82 about which it isrotatable. The gripping device 80 is disposed in a seat 84 with asemi-circular recess which essentially corresponds to the shape of thegripping device. The gripping device has a slot 86 or a groove whichextends radially inwards from the circumference. In the slot 86, whichmay be tapered, an end portion of a sheet 88 is insertable to be fixedtherein. The connection 90, i.e. the slot opening, between the sheet andthe gripping device 80 is shielded from the diaphragm of the press ofpressure cell type by the gripping device 80 being rotated so that theslot 86 and said connection 90 are oriented towards the inner wall 92 ofthe seat 84. In this way, the shielding operation is carried outessentially simultaneously with the sheet-stretching operation.

FIG. 6 b shows an upper part 100 and a lower part 102 of a grippingdevice, each provided with a recess 104 and 106, respectively. A sheet108 projecting from a forming space is disposed on the lower part 102 sothat it covers the recess 106 therein. A rotatable cylinder 110 isprovided with a radially projecting arm 112 the shape of whose end 114is complementary to the recesses. The cylinder 110 is further providedwith a radially extending protrusion 116, which in turn is articulatedto a pulling plate 118. When the pulling plate 118 is pulled in thedirection of the arrow, the protrusion 116 is actuated causing thecylinder 110 to rotate. This, in turn, causes the arm 112 to be loweredand the end 114 of the arm, together with the recess 106 in the lowerpart 102 of the gripping device, to fix the sheet 108. The upper part100 of the gripping device is then lowered, its recess 104 being fittedto the end 114 of the arm, thereby interconnecting the lower part 102and the upper part 100. The pulling plate 118, or any optional pullingmeans, such as a ram, can then pull the gripping device to stretch thesheet 108. This gripping device is conveniently used in combination witha shielding means similar to the end pieces described in connection withthe previous figures.

FIGS. 7 a and 7 b illustrate the method of handling an alternative traydevice 120. The tray device 120 shown in perspective in FIG. 7 a isforged and, thus, not made of hot-rolled sheet as the lamellar meansshown in the previous figures. Accordingly, the tray device 120 is notannularly divisible. However, the long sides are such that twobeam-shaped portions 124 a, 124 b, one on each long side, are liftablefrom the rest of the tray. Suitably, an upper part 126 a, 126 b of eachshielding member or end piece is connected to said beam-shaped portions.Thus, when the two beam-shaped portions 124 a, 124 b are lifted, theupper part 126 a, 126 b of each end piece will be lifted too, asillustrated in FIG. 7 b.

FIG. 8 illustrates only schematically the possibilities of changing thedimensions of a tray device 130. Two end pieces 132 a, 132 b arearranged on the tray bottom on either side of a forming tool 134. If asmaller forming tool is to be used, one end piece 132 b can be movedinwards to a more central position in the tray device, as indicated bythe phantom lines. The end piece 132 b is fixed in the new position in asuitable manner, for example by means of engaging means from the traybottom or additional filling elements between the end piece and theinner wall of the tray device.

The possibility of movement thus allows forming tools of different sizesto be used without the risk of the diaphragm penetrating in a spacebetween the forming tool and the end piece, which could lead tounnecessary wear of the diaphragm against the edges of these elements.

Although FIG. 8 illustrates a forged tray device, the possibility ofmovement and the change of dimension can also be applied in connectionwith other types of tray devices, such as more divisible tray deviceshaving, for example, lamellar means. In the case of a forged tray device130, in which the short sides are usually formed in one piece with thetray bottom, one short side 136 is suitably provided with a throughpassage 138. The passage 138 is formed relatively high up on the shortside 136 where the stress concentration of the tray device 130 isrelatively low. A pulling device extends through the passage, saiddevice being capable of pulling a gripping device provided in the endpiece 132 a and the sheet fixed therein.

FIGS. 9 a and 9 b are cross-sectional views of a gripping and shieldingarrangement according to one embodiment of the present invention. FIG.10 is a cut-out perspective view of the arrangement in FIG. 9 a.

With reference to FIG. 9 a, a lower shielding member 150 and an uppershielding member 152 (e.g. parts of an end piece) are shown, whichtogether form a sliding space 154 in which a gripping device comprisingand upper part 156 and a lower part 158 is slidingly arranged. The upperpart 156 of the griping device is connected to the upper shieldingmember 150, whereas its lower part 158 bears against the lower shieldingmember 152. The lower part 158 of the gripping device comprises a boss160 the shape of which fits in a recess 162 in the upper part 156. Theupper part 156 and the lower part 158 are adapted to grip and fix ablank 164, such as a sheet, which is to be formed in an adjacent formingspace. The lower part 158 of the gripping device has a groove, in whichthe vertical protrusion 172 of a horizontal plate 170 is inserted. Thus,when the plate 170 is subjected to a pulling force, the lower part 158of the gripping device will also be pulled along. When the grippingdevice is in a joined position, as shown for instance in FIG. 9 b, itwill be possible for the whole gripping device 156, 158 to be pulledalong when the plate 170 is moved, for example by means of a hydrauliccylinder.

In addition, an upwardly directed guide pin 174 is fixed to the plate.The diameter of the guide pin 174 is adapted to the diameter of a hole176 through the upper part 156 of the gripping device. Thus, the upperpart 156 of the gripping device is movable along the guide pin 174 bysaid pin being inserted in the hole 176. The guide pin 174 ensures thatthe upper part 156 and lower part 158 of the gripping device arecorrectly aligned relative to one another when brought together. In theposition of separation of the gripping device and the shielding members,as shown in FIG. 9 a, the upper part 156 of the gripping device enclosesthe top portion of the guide pin 174. This distance of separation orspace is sufficient to allow a formed blank 164 to be removed and a newone to be inserted in the arrangement. The height of the spaceessentially corresponds to the vertical extension of a processed, i.e.finished, blank, such as a sheet or any other workpiece. In the joinedposition, as shown in FIG. 9 b, the upper part 156 of the grippingdevice encloses the guide pin 174 slightly further down. In the joinedposition, space is provided for the guide pin 174 by a hollow space 180being provided in the upper shielding member 150. The guide pin 174 canbe moved horizontally in said hollow space 180 when the gripping device156, 158 is pulled to stretch the blank 164. As shown, the guide pin174, together with the horizontal plate 170 and its vertical protrusion172, further has a supplementary connecting function with respect to theupper part 156 and the lower part 158 of the gripping device.

In FIG. 10, the same reference characters are used as in FIGS. 9 a and 9b to designate corresponding parts. FIG. 10 shows how the upper part 156of the gripping device is connected to the upper shielding member 150.In the upper shielding member 150, a groove 182 is provided which isT-shaped in cross section. The upper part 156 of the gripping devicecomprises a displaceable holder in the form of a vertical pin 184 whoseupper end 186 has an enlarged diameter. The upper end 186 whose diameteris enlarged fits in the upper part of the groove 182 and thus preventsthe holder from falling down, thereby also holding the upper part 156 ofthe gripping device in place adjacent to the upper shielding member 150.The connection 190 (see FIG. 9 b) between the blank 164 and the grippingdevice is shielded when the upper shielding member 150 is pressedagainst the lower member 152, thereby making it more difficult for adiaphragm to extend between them to said connection 190.

1. A method in a press of pressure cell type comprising a forming tooland, separated therefrom, a diaphragm, which define a forming space,comprising the steps of: inserting a blank into the forming space;pressing the diaphragm against the blank, thereby forming the blankagainst the forming tool; gripping, by means of at least one grippingdevice, a blank portion projecting from the forming space; and shieldinga connection between the blank and the gripping device from thediaphragm at least when the diaphragm is pressed against the blank.
 2. Amethod as claimed in claim 1, comprising the steps of: arranging theblank between at least two gripping devices; and stretching the blank bymeans of the gripping devices, before the diaphragm is pressed againstit, so that the blank is plastically deformed.
 3. A method as claimed inclaim 2, in which said shielding is achieved by moving two shieldingmembers, one on either side of the blank, towards each other.
 4. Amethod as claimed in claim 3, further comprising the step of: grippingthe blank by moving, when the shielding members are moved towards eachother, an upper part and a lower part of the gripping device towardseach other in such manner that they fix the blank.
 5. A method asclaimed in claim 4, further comprising the step of: applying a force toat least one of the shielding members, on both sides of the horizontalextent of the blank transversely to the stretching direction, said forcebeing directed towards the other shielding member, so that an evenlydistributed pressure is exerted on the gripping device for fixing theblank.
 6. A method as claimed in claim 5, comprising the step of:keeping the two shielding members in front of the connection of theblank sufficiently separated to allow the blank to be stretched.
 7. Amethod as claimed in claim 3, further comprising the step of: applying acompressive force to the shielding members in said direction, afterstretching the blank, so that a sufficiently tight abutment against theblank is achieved in front of the connection between the blank and thegripping device to prevent the diaphragm from extending between theshielding members and the blank to said connection.
 8. A method asclaimed in claim 3, comprising the step of: stretching the blank bydisplacing the gripping device radially away from the forming space, ina space formed by the shielding members.
 9. A method as claimed in claim1, comprising the steps of: arranging the forming tool in a tray device;and effecting gripping of the blank by bringing an upper and a lowertray part together.
 10. A method as claimed in claim 9, in which thetray device comprises a tray plate and a tray frame which is annularlydivisible into at least one upper and one lower frame part, comprisingthe steps of: bringing the upper and the lower tray part together toform the tray frame, and arranging the blank in such manner that it isgripped by the upper and the lower tray part when brought together. 11.A method as claimed in claim 10, comprising the step of: separating thetray frame into the upper and the lower tray part, so that a processedblank is accessible for removal thereof, and so that, after removal ofthe processed blank, a new blank can be arranged in the tray device tobe fixed therein.
 12. A method as claimed in claim 9, further comprisingthe step of: removing the tray device from the press before the traydevice is separated into said parts.
 13. A method as claimed in claim12, further comprising the step of: inserting the tray device in thepress chamber after the separated parts have been brought together. 14.A method as claimed in claim 1, comprising the step of: turning thegripping device about an axis, so that said connection is orientedtowards a shielding wall, so as to achieve said shielding.
 15. A pressof pressure cell type, comprising: a forming tool and, separatedtherefrom, a diaphragm, which define a forming space in which a blank isintended to be formed against the forming tool by pressing the diaphragmagainst the blank; at least one gripping device arranged to grip a blankportion projecting from the forming space; and shielding means arrangedto shield the connection between the blank and the gripping device fromthe diaphragm at least when the diaphragm is pressed against the blank.16. A press of pressure cell type as claimed in claim 15, whichcomprises at least two gripping devices, the connection between theblank and at least one gripping device being movable to allow the blankto be stretched in such manner that it is plastically deformed.
 17. Apress of pressure cell type as claimed in claim 16, wherein eachgripping device comprises an upper part and a lower part, which whenbrought together are adapted to fix the blank.
 18. A press of pressurecell type as claimed in claim 17, wherein said shielding means comprisesan upper shielding member and a lower shielding member the blank beinginsertable there between.
 19. A press of pressure cell type as claimedin claim 18, wherein, in the assembled position, the shielding membersenclose the gripping device both from above and from below and define asliding space, the upper and lower shielding members having slidingsurfaces on which the upper and the lower part of the gripping device isslidable, respectively.
 20. A press of pressure cell type as claimed inclaim 19, which further comprises force-exerting means, which arearranged to exert a force on at least one of the shielding members, onboth sides of the horizontal extent of the blank transversely to thestretching direction, said force being directed toward the othershielding member, so that an evenly distributed pressure is exerted onthe gripping device for fixing the blank.
 21. A press of pressure celltype as claimed in claim 20, wherein the upper shielding member is bentin such manner that its central portion is located vertically lower thanperipheral portions on which said force-exerting means exerts saidforces, said forces straightening the upper shielding member andbringing about said even distribution of the pressure.
 22. A press ofpressure cell type as claimed in claim 20, wherein the two shieldingmembers in front of the connection of the blank are sufficientlyseparated to allow the blank to be stretched.
 23. A press of pressurecell type as claimed in claim 18, wherein the two shielding members,when brought together in front of the connection between the blank andthe gripping device, are each adapted to abut sealingly, by means of aforce exerted thereon, against a respective side of the blank to preventthe diaphragm from extending between the shielding members and the blankto said connection.
 24. A press of pressure cell type as claimed inclaim 19, wherein the upper part of the gripping device is connected tothe upper shielding member to allow them to be lifted and/or loweredtogether.
 25. A press of pressure cell type as claimed in claim 18,which further comprises a tray device, which defines a space adapted toreceive the forming tool and a blank arranged on top of the latter, thetray device being divisible into at least one upper part and one lowerpart, the upper shielding member being connected to the upper part ofthe tray device to allow them to be lifted and/or lowered together. 26.A press of pressure cell type as claimed in claim 25, wherein the traydevice comprises a tray plates and a tray frame, which tray frame isannularly divisible into at least one upper frame part and one lowerframe part, the upper shielding member being connected to the upperframe part to allow them to be lifted and/or lowered together.
 27. Apress of pressure cell type as claimed in claim 25, wherein theshielding members form part of end pieces, which are arranged at twoopposite sides of the inner wall of the tray device, said end piecesserving as a support for the forming tool.
 28. A press of pressure celltype as claimed in claim 17, wherein a hydraulic arrangement is providedcomprising a hydraulic piston and a coupling means connected thereto andto at least one of the parts of the gripping device, the hydraulicpiston being arranged to actuate the coupling means and, thus, thegripping device for stretching the fixed blank.
 29. A press of pressurecell type as claimed in claim 15, wherein the gripping device isprovided with a slot, which extends from the periphery of the grippingdevice and in which the blank portion projecting from the forming spaceis insertable.
 30. A press of pressure cell type as claimed in claim 29,wherein the gripping device is circular in cross-section and turn aboutits center axis, so that said slot, with the blank portion insertedtherein, is shielded by an at least partially enclosing wall, whosecross-section matches the gripping device.
 31. A tray device for use ina press of pressure cell type, which tray device defines a space adaptedto receive a forming tool against which a blank is formable, comprising,at least one gripping device, which is adapted to grip an end portion ofthe blank; and shielding members, which are guidable between an openposition and a shielding position and which are adapted to at leastpartially enclose the gripping device in the shielding position.
 32. Atray device as claimed in claim 31, wherein the tray device is divisibleinto at least one upper tray part and one lower tray part, the uppertray part being connected to an upper shielding member, which in turn isconnected to an upper part of the gripping device, to allow them to belifted and/or lowered together with the upper tray part and, thus,simultaneously separated from respectively a lower shielding member anda lower part of the gripping device, the lower part and the upper partof the gripping device being adapted to hold the blank between them. 33.A tray device as claimed in claim 32, comprising: at least two grippingdevices and shielding members associated therewith, wherein at least onegripping device is movable in a space formed by the upper and the lowershielding member, to allow the blank to be stretched, when gripped, sothat it is plastically deformed.
 34. A tray device as claimed in claim33, wherein force-exerting means are arranged to exert a force on theupper shielding member, on both sides of the horizontal extent of theblank transversely of the stretching direction, said force beingdirected towards the lower shielding member, so that an evenlydistributed pressure is exerted on the gripping device for fixing theblank.
 35. A tray device as claimed in claim 32, wherein the tray devicecomprises a tray plate and a tray frame, which is annularly divisibleinto at least one upper and one lower frame part, the upper shieldingmember being connected to the upper frame part to allow them to belifted and/or lowered together.
 36. (canceled)
 37. A method as claimedin claim 6, comprising the step of: exerting a pressure by thediaphragm, during its expansion towards the blank, on at least one ofthe shielding members, such that the separation is reduced and asufficiently tight abutment against the blank is achieved to prevent thediaphragm from extending between the shielding members and the blank tosaid connection.
 38. A press of pressure cell type as claimed in claim22, wherein the diaphragm is arranged to exert a pressure, during itsexpansion towards the blank, on at least one of the shielding memberssuch that the separation is reduced and a sufficiently tight abutmentagainst the blank is achieved to prevent the diaphragm from extendingbetween the shielding members and the blank to said connection.
 39. Apress of pressure cell type as claimed in claim 27, wherein at least oneof the end pieces is movable away from the inner wall towards the centerof the tray device to serve as a support for a forming tool of smallerextent.